1. Field of the Invention
The present invention relates to image projectors of a DLP (trademark) type and light sources for use in the projectors.
2. Background Art
In the past, most of image projectors use a discharge lamp such as superhigh pressure mercury lamp as a light source. However, they consume a large amount of electric power and produces a large amount of heat and a considerable amount of noise for cooling the projectors. They will be deteriorated easily unless appropriately cooled, and are expensive and not easy to use.
Recently, red, green and blue high-brightness solid light emitting diodes that produce the respective corresponding colored rays of light are widely put to practical use and tried to be used as light sources for the projectors.
Compared to the superhigh pressure mercury lamp, a single LED provides a low brightness. Thus, an important problem with a light source for the projector is how many LEDs can be disposed in a small space.
FIG. 8 shows a light source for use in the prior art projector. In this light source, seven lensed LEDs 11 are arranged at intervals of A for heat radiation purposes on a plate 10a provided at a left end of a light tunnel 10. The whole inner surface of the light tunnel 10 is made of a reflective mirror. The respective LEDs 11 emit rays of light at the divergent angle of α and are reflected by the inner surface of the light tunnel 10. The brightness distribution of the rays of light is equalized as they propagate rightward through the tunnel 10. Such rays of light are used to illuminate an optical modulator such as a digital micromirror device (trademark) (not shown), thereby forming an optical image, which is then projected through a projector lens system (not shown) onto a display screen (not shown)
With such simple regular arrangement of LEDs 11 at the intervals of A on the end of the housing, the number of LEDs to be disposed is limited. Thus, they cannot compose a light source that provides a satisfactory brightness for the projector.
Similarly, use of an array of red, green and blue LEDs as a light source is proposed. For example, Japanese Patent Publication 2003-262795 discloses an illumination panel that comprises an array of red, green and blue LEDs disposed at an inlet end of a rectangular-cross-sectional rod lens whose inner surface is optically reflective in order to provide rays of light of uniform brightness distribution. The effective panel size of this illumination panel is equal to the open end size of the rod lens, and the number of LEDs to be disposed is limited.